Impeller, centrifugal fluid machine, and fluid device

ABSTRACT

An impeller is provided with: a disk rotating about an axis; and a plurality of blades provided on the disk at intervals in a circumferential direction about the axis. Thicknesses of the blades gradually decrease from a disk side toward a tip side, and a decrease rate of the thicknesses gradually decreases from the disk side toward the tip side.

TECHNICAL FIELD

The present invention relates to an impeller, a centrifugal fluid machine including the same, and a fluid device including a plurality of centrifugal fluid machines.

Priority is claimed on Japanese Patent Application No. 2014-218191, filed Oct. 27, 2014, the content of which is incorporated herein by reference.

BACKGROUND ART

A centrifugal fluid machine such as a centrifugal compressor suctions a fluid in a casing when an impeller rotates and applies a pressure to the fluid to discharge the fluid from the casing.

Technology disclosed in Patent Literature 1 suggests an appropriate blade angle distribution of an impeller to improve performance of the impeller.

CITATION LIST Patent Literature

[Patent Literature 1]

Japanese Patent No. 4888436

SUMMARY OF INVENTION Technical Problem

With regard to an impeller of a centrifugal fluid machine, performance of impellers variously suggested as in Patent Literature 1 needs to be further improved.

Thus, the present invention is for the purpose of providing an impeller of which performance can be improved, a centrifugal fluid machine, and a fluid device.

Solution to Problem

An impeller as an aspect related to the invention to accomplish the above-described objects includes:

a disk rotating about an axis; and a plurality of blades provided on the disk at intervals in a circumferential direction about the axis and configured to guide a fluid flowing in an axial direction along which the axis extends when the plurality of blades rotate together with the disk outward in a radial direction of the axis, wherein thicknesses of the blades gradually decrease from a disk side toward a tip side, and a decrease rate of the thicknesses gradually decreases from the disk side toward the tip side in at least one region in a camber line direction serving as a direction along a camber line extending from inlet edges of the blades at a side at which the fluid flows in toward outlet edges of the blades at a side at which the fluid flows out.

In the impeller, thicknesses of the blades, which are in a portion in the height direction from the disk side toward the tip side, can be thinner than that when a rate at which the thicknesses of the blades decrease from the disk side toward the tip side is constant. Thus, in the impeller, a weight of the impeller can be reduced. Moment of inertia about the axis, that is, GD², can be reduced, and thus a load when the centrifugal fluid machine including the blades is activated can be reduced. Also, high peripheral speed durability of the impeller can be increased due to a decrease in weight of the impeller. A natural frequency of the impeller can be increased due to a decrease in weight of the impeller, and thus vibration of the impeller can be suppressed between the activation and stoppage of the centrifugal fluid machine including the blades.

Here, in the impeller, the thicknesses of the blades may gradually decrease from the disk side toward the tip side, and the decrease rate of the thicknesses may gradually decrease from the disk side toward the tip side in outlet regions which are at positions on the blades closer to the outlet edge side than intermediate positions thereof in the camber line direction and include the outlet edges.

In the impeller, a portion in the height direction of thicknesses of the blades at the outlet edges becomes thinner. Thus, a wake width of the fluid in an outlet of the impeller can be decreased.

In the impeller according to any one of the above-described aspects, the thicknesses of the blades may gradually decrease from the disk side toward the tip side, and the decrease rate of the thicknesses may gradually decrease from the disk side toward the tip side in inlet regions which are at positions of the blades closer to the inlet edge side than the intermediate positions thereof in the camber line direction and include the inlet edges.

In the impeller, a portion in the height direction of thicknesses of the blades at the inlet edges becomes thinner. Thus, shock waves of the fluid in an inlet of the impeller can be decreased.

In the impeller according to any one of the above-described aspects, the thicknesses of the blades in the entire regions of the blades in the camber line direction may gradually decrease from the disk side toward the tip side, and the decrease rate of the thicknesses may gradually decrease from the disk side toward the tip side.

In the impeller, a weight of each of the blades can be decreased over the entire region in the camber line direction. Thus, a weight of the impeller can be further decreased. Also, a portion in the height direction of thicknesses of the blades at the outlet edges becomes thinner. Thus, a wake width of the fluid in an outlet of the impeller can be decreased. A portion in the height direction of thicknesses of the blades at the inlet edges also becomes thinner. Thus, shock waves of the fluid in an inlet of the impeller can be decreased.

In the impeller according to any one of the above-described aspects, the thicknesses of the blades may gradually increase from the inlet edges toward the outlet edges and then gradually decrease in the camber line direction.

In the impeller, the thicknesses at the inlet edges and the outlet edges of the blades are thinner than those of the intermediate portions in the camber line direction. Thus, a wake width of the fluid in the outlet of the impeller can be decreased, and shock waves of the fluid in the inlet of the impeller can be decreased.

Also, an impeller as another aspect related to the invention to accomplish the above-described objects includes:

a disk rotating about an axis; and a plurality of blades provided on the disk at intervals in a circumferential direction about the axis and configured to guide a fluid flowing in an axial direction along which the axis extends when the plurality of blades rotates together with the disk outward in a radial direction of the axis, wherein thicknesses of the blades gradually increase from the inlet edges toward the outlet edges and then gradually decrease in a camber line direction serving as a direction along a camber line extending from inlet edges of the blades at a side at which the fluid flows in toward outlet edges of the blades at a side at which the fluid flows out.

In the impeller, the thicknesses at the inlet edges and the outlet edges of the blades are thinner than those of the intermediate portions in the camber line direction. Thus, a wake width of the fluid in the outlet of the impeller can be decreased, and shock waves of the fluid in the inlet of the impeller can be decreased.

In the impeller according to any one of the above-described aspects in which the thicknesses of the blades change in the camber line direction, an absolute value of a maximum decrease rate of the thicknesses of the blades in the camber line direction may be smaller than an absolute value of a maximum increase rate of the thicknesses of the blades in the camber line direction.

In the impeller, the thicknesses relatively steeply increase toward the outlet edges at the inlet edge side of the blades, and the thicknesses relatively gently decrease toward the outlet edges at the outlet edges of the blades. For this reason, in the impeller, a wake width of the fluid in an outlet of the impeller can be further decreased.

In the impeller according to any one of the above-described aspects in which the thicknesses of the blades change in the camber line direction, a rate of change of the thicknesses of the blades in the camber line direction may gradually decrease from the disk side toward the tip side.

A centrifugal fluid machine as an aspect related to the invention to accomplish the above-described objects includes:

the impeller according to any one of the above-described aspects; a cylindrical rotating shaft centering on the axis and on which the impeller is mounted; and a casing rotatably covering the impeller.

A fluid device as an aspect related to the invention to accomplish the above-described objects includes:

a plurality of centrifugal fluid machines; a rotary driving shaft; and a driving force transmission mechanism configured to transfer rotation of the rotary driving shaft to the rotating shaft of the plurality of centrifugal fluid machines.

Advantageous Effects of Invention

According to an aspect of the present invention, performance of an impeller can be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a centrifugal compressor in a first embodiment related to the present invention.

FIG. 2 is a front view of a main part of an impeller in the first embodiment related to the present invention.

FIG. 3 is a perspective view of the main part of the impeller in the first embodiment related to the present invention.

FIG. 4 is a view for describing a change in thickness according to a change in height of one of blades in the first embodiment related to the present invention.

FIG. 5 is a view for describing a change in thickness according to a change in position on one of blades in a camber line direction in the first embodiment related to the present invention.

FIG. 6 is a graph showing a change in height and a change in thickness according to a change in position in a camber line direction of one of blades in the first embodiment related to the present invention.

FIG. 7 is a cross-sectional view of a centrifugal compressor in a second embodiment related to the present invention.

FIG. 8 is a view for describing a change in thickness according to a change in height of one of blades in the second embodiment related to the present invention.

FIG. 9 is a view for describing a change in thickness according to a change in position of one of blades in a camber line direction in the second embodiment related to the present invention.

FIG. 10 is a view for describing a constitution of a geared compressor in an embodiment related to the present invention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, various embodiments of a centrifugal fluid machine related to the present invention will be described using the drawings.

First Embodiment of Centrifugal Fluid Machine

A first embodiment of the centrifugal fluid machine will be described using FIGS. 1 to 6.

The centrifugal fluid machine in this embodiment is a centrifugal compressor. As shown in FIG. 1, a centrifugal compressor 10 includes a cylindrical rotating shaft 11 centering on an axis Ar, an impeller 20 mounted on the rotating shaft 11 and rotating about the axis Ar together with the rotating shaft 11, and a casing 15 rotatably covering the impeller 20.

The impeller 20 in this embodiment is an open impeller. The impeller 20 has a disk 21 of which a shape when viewed in an axial direction Da along which the axis Ar extends has a circular shape about the axis Ar and a plurality of blades 23 provided at intervals in a circumferential direction Dc about the axis Ar.

An outer diameter of the disk 21 gradually increases from a first side in an axial direction Da toward a second side serving as an opposite side. Furthermore, the disk 21 has a shape in which tangents thereof at positions on a boundary line between a surface thereof and a meridional cross section gradually changed to face in a radial direction Dr with respect to the axis Ar from a direction substantially parallel to the axis Ar from the first side in the axial direction Da toward the second side.

As shown in FIGS. 2 and 3, the plurality of blades 23 protrude in a direction including a direction component perpendicular to the surface of the disk 21, and extend along the surface of the disk 21 from an inner side of the disk 21 in the radial direction Dr toward an outer side thereof in the radial direction Dr. The blades 23 gradually incline to one side thereof in the circumferential direction Dc from the inner side thereof in the radial direction Dr toward the outer side thereof in the radial direction Dr. The one side thereof in the circumferential direction Dc is a rear side of the disk 21 in a direction of rotation R.

Edges of the blades 23 at the first side in the axial direction Da form inlet edges 24 along which a gas flows into spaces between the plurality of blades 23. Furthermore, edges of the blades 23 at the outer side in the radial direction Dr form outlet edges 25 along which the gas flows outside of the spaces between the plurality of blades 23. Protruding directions of the blades 23 with respect to the surface of the disk 21, that is, each of ends of the blades 23 in a height direction Dh is a tip 26 and face an inner circumferential surface of the casing 15. A surface of each of the blades 23 facing a front side thereof in the direction of rotation R forms a positive pressurized surface 28, and a surface of each of the blades 23 facing the rear side in the direction of rotation R forms a negative pressurized surface 29.

As shown in FIG. 1, a cylindrical inlet flow path 16 centering on the axis Ar is formed at the first side of the casing 15 in the axial direction Da on the basis of the impeller 20. Furthermore, annular outlet flow paths 17 centering on the axis Ar are formed at positions of the casing 15 which are at the outer side of the impeller 20 in the radial direction Dr and face the outlet edges 25 of the blades 23.

As shown in FIG. 4, thicknesses of the blades 23 of the impeller 20 gradually decrease from a disk side toward a tip side. Furthermore, a decrease rate of each of the thicknesses gradually decreases from the disk side toward the tip side. Here, center lines Lc of the thicknesses extend in a direction perpendicular to the surface of the disk 21 in FIG. 4. This is because a change in thickness of the blades 23 according to a change in position of the blade 23 in the height direction Dh is then easily understood. Actually, the center lines Lc of the thicknesses are inclined with respect to the surface of the disk 21 at at least some positions between the inlet edge 24 and each of the outlet edges 25. In addition, the center lines Lc of the thicknesses are curved at at least some positions therebetween. As shown in FIG. 3, the thickness of the blade 23 in this embodiment corresponds to a diameter of a circle Cc in contact with the positive pressurized surface 28 and the negative pressurized surface 29 of the blade 23 centering on a camber line CL of the blade 23. Note that the camber line CL is a line obtained by connecting points which are the same distance away from the positive pressurized surface 28 of the blade 23 and the negative pressurized surface 29 thereof and extending from the inlet edge 24 toward the outlet edge 25 of the blade 23. The camber line CL is present for each position of the blade 23 in the height direction Dh.

As shown in FIG. 5, the thicknesses of the blades 23 gradually increase and then gradually decrease from the inlet edge 24 toward the outlet edges 25 in a camber line direction Dcl along the camber line CL.

Here, the change in position in the height direction Dh and the change in thickness of the blade 23 according to a change in position in the camber line direction Dcl will be described using FIG. 6. Note that a horizontal axis of FIG. 6 indicates a percentage of distances between the inlet edge 24 and positions in the camber line direction Dcl when a distance between the inlet edge 24 and the outlet edge 25 along the camber line CL is set to be 100%. Furthermore, a vertical axis of FIG. 6 indicates a rate of thicknesses at positions in the height direction Dh with respect to the maximum thickness in the height direction Dh. Curves in FIG. 6 are thickness curves obtained by connecting positions at which rates of distances from a disk-side edge 27 with respect to distances between the disk-side edge 27 and the tip 26 of the blade 23 in the height direction Dh are the same. Among the thickness curves, a thick solid line is a thickness curve at a position at which a distance ratio of the blade 23 in the height direction Dh is 0, that is, the disk-side edge 27. Here, a dotted line is a thickness curve at a position at which the distance ratio of the blade 23 in the height direction Dh is 0.2. A two-dot chain line is a thickness curve at a position at which the distance ratio of the blade 23 in the height direction Dh is 0.4. A dashed line is a thickness curve at a position at which the distance ratio of the blade 23 in the height direction Dh is 0.6. A one-dot chain line is a thickness curve at a position at which the distance ratio of the blade 23 in the height direction Dh is 0.8. A thin solid line is a thickness curve at a position at which the distance ratio of the blade 23 in the height direction Dh is 1.0, that is, the tip 26.

As shown in FIG. 6, a thickness of the blade 23 at a position at which a distance ratio of the disk-side edge 27 is 0, that is, the disk-side edge 27, is the thickest at each position in the camber line direction Dcl when compared to any position in the height direction Dh. Furthermore, a thickness of the blade 23 at a position at which the distance ratio of the disk-side edge 27 is 1, that is, the tip 26, is the thinnest at each position in the camber line direction Dcl when compared to any position in the height direction Dh. As described above using FIG. 4, the thickness of the blade 23 gradually decreases as the distance ratio of the disk-side edge 27 increases, that is, toward the tip side. The decrease rate of the thicknesses gradually decreases from the disk side toward the tip side.

As shown in FIG. 6, as described above using FIG. 5, the thickness of the blade 23 gradually increases and then gradually decreases from the inlet edge 24 toward the outlet edges 25 at any position in the height direction Dh. Moreover, as clearly shown as the thickness curve (the thick solid line) at the position at which the distance ratio of the disk-side edge 27 is 0 and the thickness curve (the dotted line) at the position at which the distance ratio of the disk-side edge 27 is 0.2 in FIG. 6, an absolute value of a maximum increase rate ΔTimax of the thicknesses in the camber line direction Dcl is greater than an absolute value of a maximum decrease rate Tdmax of the thicknesses in the camber line direction Dcl. In other words, at the inlet edge 24 side of the blade 23, each of thicknesses thereof relatively steeply increases toward the outlet edges 25, and at the outlet edges 25 side of the blade 23, each of thicknesses thereof relatively gently decreases toward the outlet edges 25. A change rate of the thickness in the camber line direction Dcl gradually decreases from the disk side toward the tip side.

As described above, in this embodiment, the thickness of the blade 23 gradually decreases from the disk side toward the tip side in the entire region thereof in the camber line direction Dcl. Moreover, the decrease rate gradually decreases from the disk side toward the tip side. For this reason, in this embodiment, a thickness of the blade 23, which is in a portion in the height direction Dh in the entire region thereof in the camber line direction Dcl, can be thinner than that when a rate at which the thickness of the blade 23 decreases from the disk side toward the tip side is constant. Thus, in this embodiment, a weight of the impeller 20 can be reduced. The moment of inertia about the axis Ar, that is, GD², can be reduced, and thus a load when the centrifugal compressor 10 is activated can be reduced. High peripheral speed durability of the impeller 20 can be increased due to a decrease in weight of the impeller 20. A natural frequency of the impeller 20 can be increased due to a decrease in weight of the impeller 20, and thus vibrations of the impeller 20 can be suppressed between the activation and stoppage of the centrifugal compressor 10.

In this embodiment, a thickness of the blade 23 at the inlet edge 24, which is in a portion in the height direction Dh, is thinner than that when the rate at which the thickness of the blade 23 decreases from the disk side toward the tip side is constant, and the thickness of the blade 23 gradually becomes thicker from the inlet edge 24 toward the outlet edges 25 at the inlet edge 24 side. For this reason, in this embodiment, shock waves of the gas in an inlet of the impeller 20 can be minimized, and thus aerodynamic performance can be improved.

Also, in this embodiment, a thickness of the blade 23 at outlet edges 25, which is in a portion in the height direction Dh, is thinner than that when the rate at which the thickness of the blade 23 decreases from the disk side toward the tip side is constant, and the thickness of the blade 23 gradually becomes thinner toward the outlet edges 25 at the outlet edges 25 side. For this reason, in this embodiment, a wake width of the gas in an outlet of the impeller 20 can be decreased. Particularly, in this embodiment, a change ratio of the thicknesses in the camber line direction Dcl at the outlet edges 25 side of the blade 23 is smaller than a change ratio of the thicknesses in the camber line direction Dcl at the inlet edge 24 side of the blade 23. Thus, the wake width of the gas in the outlet of the impeller 20 can be more effectively decreased, and thus aerodynamic performance can be increased.

Second Embodiment of Centrifugal Fluid Machine

A second embodiment of a centrifugal fluid machine will be described using FIGS. 7 to 9.

The centrifugal fluid machine in this embodiment is also a centrifugal compressor. As shown in FIG. 7, a centrifugal compressor 10 a in this embodiment also includes a cylindrical rotating shaft 11 centering on an axis Ar, an impeller 20 a mounted on the rotating shaft 11 and rotating about the axis Ar together with the rotating shaft 11, and a casing 15 rotatably covering the impeller 20 a as in the first embodiment. Furthermore, the impeller 20 a has a disk 21 and a plurality of blades 23 a as in the impeller 20 of the first embodiment. Here, the impeller 20 a in this embodiment is a closed impeller. For this reason, shrouds 22 are provided at tips 26 of blades 23 a. In other words, the plurality of blades 23 a are disposed between and connected to a disk 21 and the shrouds 22.

As shown in FIG. 8, thicknesses of each of the blades 23 a of the impeller 20 a are substantially the same at any position of the blade 23 a in a height direction Dh. Furthermore, as shown in FIG. 9, the thickness of the blade 23 a of the impeller 20 a gradually increases and then gradually decreases from an inlet edge 24 toward an outlet edge 25 in a camber line direction Dcl along a camber line CL as in the blade 23 a of the first embodiment. Moreover, an absolute value of a maximum increase rate ΔTimax of thicknesses in the camber line direction Dcl is greater than an absolute value of a maximum decrease rate Tdmax of thicknesses in the camber line direction Dcl. In other words, at the inlet edge 24 side of the blade 23 a, each of thicknesses thereof relatively steeply increases toward the outlet edge 25, and at the outlet edge 25 side of the blade 23 a, each of thicknesses thereof relatively gently decreases toward the outlet edge 25.

For this reason, also in this embodiment, as in the first embodiment, shock waves of a gas in an inlet of the impeller 20 a can be minimized, and a wake width of the gas in the outlet of the impeller 20 a can be decreased. Thus, also in this embodiment, aerodynamic performance of the impeller 20 a can be improved.

Embodiment of Fluid Device

An embodiment of a fluid device will be described using FIG. 10.

As a fluid device, as shown in FIG. 10, there is a fluid device including a rotary driving shaft 31, a plurality of centrifugal compressors 10 x, 10 y, and 10 z, and a driving force transmission mechanism 32 configured to transfer rotation of the rotary driving shaft 31 to rotating shafts 11 x, 11 y, and 11 z of the plurality of centrifugal compressors 10 x, 10 y, and 10 z. The driving force transmission mechanism 32 has a driving gear 33 provided at the rotary driving shaft 31, driven gears 34 provided at the rotating shafts 11 x, 11 y, and 11 z of the centrifugal compressors 10 x, 10 y, and 10 z, and transmission gears 35 configured to transfer rotation of the driving gear 33 to the driven gears 34. The driving force transmission mechanism 32 transfers the rotation of the rotary driving shaft 31 to the rotating shafts 11 x, 11 y, and 11 z of the centrifugal compressors 10 x, 10 y, and 10 z via the gears 33, 34, and 35 so that the rotation of the rotary driving shaft 31 is accelerated. Thus, the driving force transmission mechanism 32 serves as a speed increasing gear.

One or more centrifugal compressors 10 x of a first stage among the plurality of centrifugal compressors 10 x, 10 y, and 10 z suction the gas from the outside and increase a pressure of the gas. One or more centrifugal compressors 10 y of a second stage among the plurality of centrifugal compressors 10 x, 10 y, and 10 z further increase the pressure of the gas increased by the centrifugal compressor 10 x of the first stage. A centrifugal compressor 10 z of a third stage further increases the pressure of the gas increased by the centrifugal compressor 10 y of the second stage and discharges the gas to the outside. For this reason, in this fluid device, a discharge port of the centrifugal compressor 10 x of the first stage is connected to a suction port of the centrifugal compressor 10 y of the second stage using pipes 37, and a discharge port of the centrifugal compressor 10 y of the second stage is connected to a suction port of the centrifugal compressor 10 z of the third stage using a pipe 38.

As described above, the fluid device, in which the rotating shafts 11 x, 11 y, and 11 z of the plurality of centrifugal compressors 10 x, 10 y, and 10 z and the rotary driving shaft 31 are coupled to each other using the driving force transmission mechanism 32 and the centrifugal compressors 10 x, 10 y, and 10 z of the stages sequentially increase the pressure of the gas, is referred to as a geared compressor. Hereinafter, this type of fluid device is referred to as a geared compressor 30.

An impeller with a large flow coefficient is used for the centrifugal compressor 10 x of the first stage of the geared compressor 30. A machine Mach number in such an impeller may be maximally about 1.3 (an impeller peripheral speed of 430 m/s under atmospheric suction conditions) in some cases. Thus, high peripheral speed durability and high aerodynamic performance are needed in such an impeller.

In this embodiment, as the centrifugal compressor 10 x of the first stage, the centrifugal compressor of the above-described first or second embodiment is used.

Note that, although this embodiment is an example in which the centrifugal compressor of the above-described first or second embodiment is used for only the centrifugal compressor 10 x of the first stage, the centrifugal compressor of the above-described first or second embodiment may be used for the centrifugal compressor 10 y of the second stage or the centrifugal compressor 10 z of the third stage as well. Also, although the geared compressor 30 in this embodiment is an example in which the geared compressor 30 has the centrifugal compressors 10 x, 10 y, and 10 z of the first to third stages, the geared compressor may have centrifugal compressors of only the first and second stages or may have centrifugal compressors of a fourth stage or more.

Modified Example

In the first embodiment, the thickness of the blade 23 gradually decreases from the disk side toward the tip side in the entire region in the camber line direction Dcl. Moreover, the decrease rate thereof gradually decreases from the disk side toward the tip side. However, the thickness of the blade 23 may gradually decrease from the disk side toward the tip side and the decrease rate thereof may gradually decrease from the disk side toward the tip side in only an outlet region which is at a position of the blade 23 closer to the outlet edge 25 side than an intermediate position thereof in the camber line direction Dcl and includes the outlet edge 25. Also, the thickness of the blade 23 may gradually decrease from the disk side toward the tip side and the decrease rate thereof may gradually decrease from the disk side toward the tip side in only an inlet region which is at a position of the blade 23 closer to the inlet edge 24 side than the intermediate position thereof in the camber line direction Dcl and includes the inlet edge 24 or only the inlet region and the above-described outlet region.

In the second embodiment, the thickness of the blade 23 a is substantially the same at any position in the height direction Dh. However, also with regard to the blade 23 a of the closed impeller like the second embodiment, the thickness of the blade may gradually decrease from the disk side toward the tip side in at least one region thereof in the camber line direction Dcl, and the decrease rate thereof may gradually decrease from the disk side toward the tip side as in the first embodiment.

The above-described embodiments are all examples in which the centrifugal fluid machine is the centrifugal compressor. However, the present invention is not limited to a centrifugal compressor as long as a device is a centrifugal fluid machine and may be, for example, a centrifugal pump.

INDUSTRIAL APPLICABILITY

According to an aspect related to the present invention, performance of an impeller can be improved.

REFERENCE SIGNS LIST

-   -   10, 10 a, 10 x, 10 y, 10 z Centrifugal compressor (centrifugal         fluid machine)     -   11, 11 x, 11 y, 11 z Rotating shaft     -   15 Casing     -   20, 20 a Impeller     -   21 Disk     -   22 Shroud     -   23, 23 a Blade     -   24 Inlet edge     -   25 Outlet edge     -   26 Tip     -   27 Disk-side edge     -   28 Positive pressurized surface     -   29 Negative pressurized surface     -   30 Geared compressor (fluid device)     -   Ar Axis     -   CL Camber line     -   Da Axial direction     -   Dc Circumferential direction     -   Dcl Camber line direction     -   Dh Height direction     -   Dr Radial direction 

1. An impeller comprising: a disk rotating about an axis; and a plurality of blades provided on the disk at intervals in a circumferential direction about the axis and configured to guide a fluid flowing in an axial direction along which the axis extends when the plurality of blades rotate together with the disk outward in a radial direction of the axis, wherein thicknesses of the blades gradually decrease from a disk side toward a tip side, and a decrease rate of the thicknesses gradually decreases from the disk side toward the tip side in at least one region in a camber line direction serving as a direction along a camber line extending from inlet edges of the blades at a side at which the fluid flows in toward outlet edges of the blades at a side at which the fluid flows out, and the thicknesses of the blades gradually increase from the inlet edges toward the outlet edges and then gradually decrease in the camber line direction.
 2. The impeller according to claim 1, wherein the thicknesses of the blades gradually decreases from the disk side toward the tip side, and the decrease rate of the thicknesses gradually decreases from the disk side toward the tip side in outlet regions which are at positions of the blades closer to the outlet edge side than intermediate positions thereof in the camber line direction and include the outlet edges.
 3. The impeller according to claim 1, wherein the thicknesses of the blades gradually decreases from the disk side toward the tip side, and the decrease rate of the thicknesses gradually decreases from the disk side toward the tip side in inlet regions which are at positions of the blades closer to the inlet edge side than the intermediate positions thereof in the camber line direction and include the inlet edges.
 4. The impeller according to claim 1, wherein the thicknesses of the blades in the entire regions of the blades in the camber line direction gradually decrease from the disk side toward the tip side, and the decrease rate of the thicknesses gradually decreases from the disk side toward the tip side. 5-6. (canceled)
 7. The impeller according to claim 1, wherein an absolute value of a maximum decrease rate of the thicknesses of the blades in the camber line direction is smaller than an absolute value of a maximum increase rate of the thicknesses of the blades in the camber line direction.
 8. The impeller according to claim 1, wherein a change ratio of the thicknesses of the blades in the camber line direction gradually decreases from the disk side toward the tip side.
 9. A centrifugal fluid machine comprising: the impeller according to claim 1; a cylindrical rotating shaft centering on the axis and on which the impeller is mounted; and a casing rotatably covering the impeller.
 10. A fluid device comprising: a plurality of centrifugal fluid machines according to claim 9; a rotary driving shaft; and a driving force transmission mechanism configured to transfer rotation of the rotary driving shaft to the rotating shaft of the plurality of centrifugal fluid machines. 